Aluminum alloy



Patented Aug. 17, 1926.

UNITED STATES 1,596,020 PATENT OFFICE.

ALADAR PAGZ, OF CLEVELAND, OHIO, ASSIGNOR TO THE ALUMINUM COMIPANY OF AMERICA, 01 PITTSBURGH, PENNSYLVANIA. A CORPORATION OF PENNSYLVANIA.

ALUMINUM ALLOY.

No Drawing. Original application filed September 15, 1922, Serial No. 588,491. Divided and thil appli v cation filed April 19, 1924. Serial No. 707,569.

This invention relates-to aluminum alloys, particularly those containing silicon. Its chief object is to provide a method of making castings of such alloys which will improve their physical properties. The invention is based on the discovery that aluminum alloys, especially those containing silicon in substantial amounts, have their physical properties, especially tensile strength and ductility, improved by treat ment with a reducible oxygen-containing compound of an alkali metal.

In my prior U. S. Patent No. 1,387,900, aprocess is described for treating aluminum-silicon alloys with fluorine compounds of an alkali metal; by that treatment the grain size of the resulting casting is greatly refined and'the strength and ductility increased. It has also become known (U. S- Patent No.,1,410,461) that a similar grainrefining efiect, with its consequent improvement in the physical properties of the alloys, can be effected bythe introduction into the molten alloy of either metallic sodium or potassium or both. There is reason to believe that when an aluminum alloy in the molten condition is treated with an alkali fluoride, such as sodium or potassium 'fluoride, that a reaction takes place between the alkali metal compound and the aluminum of the alloy, which results in decomposition of the fluoride and the formation of metallic sodium or potassium incontact with the alloy. Apparently it is this alkali metal which effects the observed improvement in physical properties.

Not all alkali metal compounds are reduced by' aluminum or. reduced with sufiicie'nt rapidity or completeness at suitable temperatures to effect the desired changes; In addition to the class oftrefining compounds just referred to, and which contain fluorine, I have discoveredthat sodium hydroxide or potassium hydroxide, or a reducible mixture of oxygen-containing compounds of sodium or potassium will produce the desired refining effect on aluminum-silicon alloys, and under certain conditions are particularly well adapted for this purpose.

In carrying out this invention in the vpreferred manner, an alloy of aluminum and silicon,oontaining from 3 to 15 percent silicon approxlmately,

manner, as for example, by stirring metallic molten alloy is prepared in a suitable silicon into molten aluminum and allowing it to dissolve. Aluminum base alloys containing from 8 to 13 percent silicon have especial y desirable properties conferred on them by treating by my process.

I add sodium or potassiumhydroxide equivalent toat least 0.5 percent but preferably somewhat. more of free alkali metal. This compound is incorporated inthe alloy, as'for example, by vlgorous stirring. After the reaction has been completed, the alloy is skimmed and cast in the usual manner. On standing the reduction products tend to be eliminated from the molten all-0y so that eventually the capacity for improvement on casting diminishes. If the highestphysical properties are desired, the molten alloy should be cast with reasonable promptness after treatment with the alkali metal oxide compound has been completed.

The sodium hydroxide can be advantageously mixed with other substances which overcome, in some degree at least, its hygroscopic tendency. For example, I may melt the caustic soda with sodium chloride, calcium fluoride, sodium fluoride, calcium oxide, etc. One convenient method of adding' the sodium hydroxide or refining mixture to the alloy is to maintain a separate pot of the fused compound. A'cold carbon rod orother suitable stirring rod can then be dipped into the. molten sodium hydroxide, for example, and a quantity of the sodium hydroxide allowed to freeze upon the stirring rod, after which it can be transferred to the molten aluminum alloy and in corporated by vigorously stirring it therein.

Apparently the action of the aluminum is to combine with the oxygen of the sodium hydroxide to liberate nascent metallic sodium in contact with the alloy. It is not necessary, in fact, that sodium hydroxide be used, for other mixtures such as sodium carbonate and lime, or sodium carbonate and a reducing agent which would form the equivalent of sodium oxide in the alloy, can be eflectively employed. The addition of the alkali metal in the form of a conipound,-rather than in elemental form, seems to be advantageous in securing thorough dissemination of the alkali metal throughout the alloy. Furthermore, the energy of the reaction seems to form oxide of aluminum and To the tember 12th, 1919,

serve in spreadin the active principles throughout the al oy, and the reduction products other than alkali metal appear to assist in the refining action which is observed. I do not commitmyself, however, in any way to any particular theory or explanation of the observed phenomenon. Neither do I limit myself to the exclusion of metals other than aluminum and silicon (with their customary impurities, but include within the scope of "my process such desirable for special purposes. ThusI have Ifloulilild my improved grain-refining rocess 1 al mi hum-silicon-copper alloy described and claimed in my applicationfiled Sep- Serial Number 323,350, and in combination with the aluminum-silicon-manganese alloy described and claimed in my application filed February 27th, 1922,

Serial Number 539,740, and incombination with the aluminum-silicon-cobalt alloy described and claimed in my application filed April 3rd, 1922, Serial Number 549,203.

The term alkali metal or compound as employed in the specifications and claims includes sodium and potassium only.

The invention herein setforth has been disclosed in my pending application Serial No. 588,491 filed September 15, 1922, of which this is a division.

Having thus described my invention so that those skilled in the art may practice the same, what I desire to secure by Letters Patent is defined in what I claim.

What I claim is: 4 v

1. The method of making aluminum base alloy castings comprisin preparing an alloy containing not less t an about 3 percent nor more than 15 percent ofisilicon, treating the molten alloy with a reagent containing an oxygen-containing compound of an alkali metal capable of being reduced in the molten alloy, solidify while it stillcontains sufficient of the reduction products to produce an implriovement in the physical properties of the a oy. I

2. The method of making aluminum base alloy castings comprising preparing an alloy containing from about 8 to 13 percent of silicon, treating the molten alloy with "areagent containing an oxygen-containing compound of an alkali metal reducible 1n the molten alloy, and casting the alloy while it still retains suflicient of the reduction products to favorably afiect the physical properties of the alloy.

3. The method of making aluminum base alloy castings comprising preparing an alloy advantageous in connection with theand causing the alloy to- 4. The method of producing aluminum.-

base alloys which contain silicon in substantial amount, which comprises the step of introducing into-the molten alloy a reagent including a reducible oxygen containing compound of sodium capabe of being reduced in the molten alloy.

5. The method of producing aluminum base alloys containing silicon-in substantial amount, which comprises the step of int-roducing into the molten alloy. a reagent comprising alkali metal hydroxide.

6. The method of producing aluminum base alloys containing silicon-in substantial amount, which comprises the step of introducing into the molten alloy a reagent comprising sodium hydroxide.

7. The method of making aluminum silicon alloy castings having improved physical properties which comprises preparing a molten alloy containing a substantial amount of silicon, incorporating in the molten alloy an oxygen-containing compound of an alkali metal capable of being reduced in the molten alloy, and then casting the alloy with reasonable promptness.

8. The method of making a silicon-containing aluminum alloy casting having improved physical properties which comprises preparing a molten alloy containing a substantial amount of silicon, melting a reagent containing a reducible, oxygen-containing compound of an alkali metal, coating a stirring rod with the molten reagent, transferring the coated rod to the molten alloy and stirring the molten metal therewith, and casting the alloy'with reasonable prom tness after the stirring.

9. he method of making a silicon-containin prov physical properties which comprises preparinga molten allo containin a substantial amount of' silicon, treating the molten alloy with an oxygen-containing alkali metal compound capable of being reduced to metallic form in the molten alloy, and casting the alloy before substantially all the reduction products have been eliminated therefrom.

In testimony whereof I hereunto aifix my signature this 16th day of April, 1924.

ALADAR PACZ.

aluminum alloy casting having im- 

